6G6 EEPOET— 1893. 



machinery having reciprocating parts may be referred to ; sacli, for 

 instance, as some classes of mining machinery, sorting and grading machi- 

 nery as nsed in flour mills, some textile machinery, paper-making machi- 

 nery, coal screens, and the like. In all the machines of this class the 

 push and pull of the reciprocated part is attended by a corresponding 

 pull and push against that part of the machine framing to which the 

 bearings of the crank or other reciprocating medium are fixed. As far as 

 possible, this is compensated by the use of balance weights on the crank 

 shaft, but in many cases the motion which would otherwise be set up has 

 to be opposed by the costly method of constructing very strong framing, or 

 the often inconvenient one of employing guy ropes or stays ; a method which 

 often gives rise to vibration in the building to which these stays are attached. 

 After attempting to prevent vibrations thus set up and to conquer this 

 hete noire of mechanical engineering, the author has found that the best 

 way to conquer it is to make use of it — -to convert this mechanical by- 

 product into a mechanical servant. This can be done in a large number 

 of cases. Where, for instance, a part of a machine is reciprocated by 

 means of a crank and connecting rod, the weight of which is balanced by 

 rotating weights on the crank shaft, the whole of the vibration in the 

 framing of the machine may be avoided by dispensing entirely with the 

 crank and connecting rod, and using only the rotating balance weights 

 on a shaft running in bearings which are attached, not to the framing, but 

 to the thing which has to be reciprocated or gyrated. The crank and 

 oonnecting rod being absent, the balance weights are now unbalanced 

 except dynamically, and the want of balance is kinetically equivalent to 

 the required motion in the thing to be gyrated. This was shown by 

 the models placed upon the table, and by reference to a simple case as 

 shown by the diagram exhibited. 



The relation between the range of reciprocation or gyration of the part 

 to be operated and of the rotating unbalanced weight, as well as of their 

 respective weights, may be represented by the following expressions : — 



If R^radius of gyration of part moved, 



r= radius of unbalanced rotating weight, 

 W= weight of part to be moved, 

 t<;=weight of rotating part (W in the figures), 

 then 



=— ; r=Rx— . 



K w w 



R= ^ 



and 



"W==; XVJ ; W= 



w 



R 



(a) 



In the diagram is shown a suspended screen operated in the manner 

 described by a perfectly free rotating weight. Fig. 1 is a plan of such a 

 screen ; fig. 2, an elevation of the same with the frame partly in sec- 

 tion ; fig. 3, an end elevation of the same ; fig. 4, an elevation to a larger 

 scale of the bearing carrying the rotating weight ; and fig. 5, the short 

 spindle bracket and pulley by means of which, through the medium of a 



